This invention relates to a method of packaging a nuclear reactor vessel for decommissioning and removal, and more particularly, to a method wherein low density concrete (in a wet mixture) is injected into the vessel and external radiation shielding of different thicknesses is mechanically attached to the vessel and then welded to itself to reduce the cost of removal of a reactor vessel.
Various methods for disposing of nuclear reactor pressure vessels (xe2x80x9cRPV""sxe2x80x9d) exist. As described in American Nuclear Society Transactions, (November 1999), RPV""s may be disposed of by segmenting the RPV into small pieces and placing the pieces into liners and shielded casks for transport to disposal sites or by placing an entire RPV inside a shielded transport cask.
These methods are extremely costly and are not always suited for the disposal of large full-size ( greater than 900 MW(electric)) RPV""s. For example, the known methods may result in high fabrication and transportation costs, high grouting, shielding and burial site disposal volumes, and often high worker radiation doses.
It is therefore an object of the present invention to provide a method of packaging a nuclear reactor vessel for decommissioning and removal which reduces cost and which can be implemented on large full-size RPV""s without incurring the foregoing disadvantages.
The object of the invention can be attained and the disadvantages of the prior methods can be overcome by providing a method of packaging a nuclear reactor vessel for decommissioning and removal, including the steps of: installing reactor vessel permanent closure plates onto the vessel; injecting concrete into the vessel; installing a first ring of shielding material around the main nozzles of the vessel; enclosing the vessel core area with a second shielding ring; welding longitudinal seams of the first shielding ring; welding longitudinal seams of the second shielding ring; welding the second shielding ring to the first shielding ring; placing the vessel on shipping cradles; and tightening a longitudinal restraint mechanism to the vessel. The method can also include the step of installing impact limiters on each end of the vessel.
The concrete injected into the vessel can be wet, low density cellular concrete or the like with a density between 0.721 g/cm3 to 1.041 g/cm3 and can be prepared with foaming agents and curing additives on the site where the decommissioning is to take place. The concrete is allowed to harden prior to final closure and sealing of all the reactor openings.
The method of packaging the nuclear reactor vessel also includes the step of circulating air into the vessel to remove heat from inside the vessel, which is performed prior to the step of injecting concrete into the vessel. In addition, prior to installing the first shielding ring, the method of packaging a nuclear reactor vessel for decommissioning and removal can include the steps of: allowing the vessel to vent and cool; removing temporary closure plates; verifying that the vessel includes a requisite amount of the concrete; verifying that there are no empty spaces in the vessel; and confirming that no free standing water is in the vessel.
The first and second shielding rings can preferably be of steel, or the like, and in a preferred embodiment have respective thicknesses sized to provide the requisite amount of radiation shielding. The second shielding ring can be applied to the vessel by lowering the vessel into the second shielding ring and mechanically fastening the second shielding ring to the vessel. The closure plates are preferably made of steel and can be welded to the vessel.